altieri



July 9, 1963 J. v. ALTIERI, JR 3,096,548

SPECIAL TECHNIQUEIFOR CASTING IMPELLER BLADE PASSAGES Filed Dec. 8, 1960 2 Sheets-Sheet 1 a FIG.

\ Br nQ FM/AAJ A TTORNEY y 1963 J. v. ALTIER], JR 3,096,548

SPECIAL TECHNIQUE FOR CASTING IMPELLER BLADE PASSAGES Filed Dec. 8. 1960 2 Sheets-Sheet 2 INVENTOR JAMES m1. TIER! JR.

ATTORNEY X A a Z, m My. w w w %/////%///WM H z 3,096,548 SPECIAL TECHNIQUE FOR CASTING INIPELLER BLADE PASSAGES James V. Altieri, Jr., Hamden, Conn., assignor to United This invention relates to multibladed cast impellers having complex three-dimensional blading and has as one of its objects an improved method of making such impellers. Heretofore, it has been the practice to make a complete master impeller by hand from which production impellers were cast. This is an exacting and timeconsuming operation since the pressure and suction surfaces of each blade, involving compound curvature, must be shaped to the required dimensions and all of the several blades must be identical in form.

A principal object of this invention is, accordingly, to provide an improved method by which it is possible to cast impellers of complex blading without the necessity of making a complete hand-shaped master impeller.

If the impeller has -a large number of blades which are closely spaced, it is very diflicult to shape adjacent pressure and suction surfaces of the master impeller blades. As the number of blades is increased and the interblade spaces become narrower, it'be'comes vintually impossible to shape these surfaces.

Another object of this invention is to provide a method for making a multibladed impeller which requires hand shaping of only the hub and a single blade of the master impeller, the pressure and suction surfaces of which are readily accessible for shaping.

A further object of this invention is to provide a method of making cast impellers of this type which clearly simplifies the handwork required in making the master impeller and which produces an impeller, the blades of which are identical. 1

Some impellers have such a high angle of blade wraparound that any mold made has to be destroyed in removing the impeller from the mold.

It is a further object of this invention to provide a method for making a mold for casting such impellers in which the mold is so simple and inexpensive to produce that it is expendable.

A still further object of this invention is generally to improve upon existing methods of making complex cast impellers.

These and other objects and advantages of the invention Will be apparent or will be pointed out in connection with the following detailed description of the novel method of this invention shown in the accompanying drawings. In these drawings:

FIG. 1 is a side elevation of the hub and a single impeller blade comprising the master impeller;

FIG. 2 is a vertical sectionthrough a female mold made by rotation of the master impeller about its axis of rotation; 7

FIG. 3 is a similar view showing a plaster impression on the pressure surface of the blade;

FIG. 4 is a similar view in which the plaster impression of FIG. 3 has been indexed counterclockwise 300 to the next blade position on the opposite, or suction, side of the master blade;

FIG. 5 is a somewhat schematic transverse section of FIG. 3;

FIG. 6 is a schematic transverse section of FIG. 4 after the space between the impression and the master blade has been filled; p

. FIG. 7 is a schematic transverse section of the mold United States Patent "ice of FIG. 2 with the interblade core members in place, ready for casting the impeller; and

FIG. 8 shows a Side elevation of a finished impeller casting with the hub tip in place.

In practicing the method of this invention, the hub 8 of the impeller is first generated and a single impeller blade 10 is then formed thereon. The blade may be fabricated of the same material as the hub, which is ,usually wood. It may be made of any moldable material which can be readily worked to the desired shape and then allowed to harden. The suction surface A of the blade is carefully shaped using template-s, after which the pressure surface B is likewise shaped. This work can be accomplished with great facility since the surfaces are fully accessible.

An excellent method of shaping the hub :and single blade of the master impeller, shown in FIG. 1, is described and claimed in an application of George H. Nutter and Glenn M. Wood, Serial No. 766,304, filed October 9, 1958, and copend-ing with this application. This copending application issued on May 30, 1961, as Patent No. 2,985,952.

The single-bladed master impeller is first used to make the female mold shown in FIG. 2. Here a mold box 12 has been filled with a moldable material 14 in which the master impeller has been rotated about its axis of rotation to form the mold cavity 16. This mold is then allowed to harden. The material 14 may be any of the well-known refractory molding materials, for example, oxides of magnesium or aluminum, or a plastic material may be used which is coated with a ceramic slurry. Either will result in a refractory mold suitable for casting articles of high-fusing metals and alloys.

The particular impeller illustrated has a truncated skirt. This may be cut oil later from the cast impeller or, as shown, may be cut off the master impeller. In this case, an annular core 13 must be provided, as shown in FIG. 2, when the mold is poured. The terms pouring the mold or when the mold is poured whenever they occur in this specification and claims refer to pouring molten casting metal into a mold cavity.

Next, an impression is made of the pressure surface B of blade 10, as shown in FIGS. 3 and 5. As indicated in FIG. 3, the impression is preferably taken while the master impeller is in the female mold. In taking this impression a relatively thin body of plaster or ceramic material 18 is built up on the pressure side B of master blade 10. The body 18, when dry, is then removed with the master impeller from the female mold. The impression 18 is then removed from the blade surface B and the blade and the impression are replaced in the female mold with'the impression 18 translated counterclockwise (as viewed in FIG. 6) relative to the blade 10, through an angle which will locate the surface impression of the pressure surface B of the blade where the pressure surface of the next adjacent blade would be, as shown in FIG. 6. Here, the blade 10 has been replaced in the female mold and the surface impression has been translated until it is from the pressure surface of the master blade to produce the correct blade to blade spacing for a sixbladed impeller;

Ilhe space between the body 18 and the suction surface A of master blade 10 is filled with a second body of plastea or ceramic material 20 'to form an interblade mold member 22 which includes the body 18. Since the spiral body .18 tends to wedge between opposed tapered surfaces on the female mold and the hub 8 of the master impeller, no special positioning means is required to hold it in place during the pouring of member 22.

When the body 20 has set, the unitary piece 22, comprising bodies 18 and 20, provides a core of the interblade passage between the suction side A of one blade of the impeller and the pressure side B of the next adjacent blade of the impeller. This interblade core member, if of nonrefractory material, is then removed from the female mold and coated with a ceramic slurry to produce a refractory core surface. This procedure is repeated, using the master impeller hub and blade, until six of these identical inter-blade passage cores have been made, since the impeller to be cast is a six-bladed impeller.

It will be clear from the above that for a six-bladed propeller six interblade mold members 22 will be made, one at a time, utilizing the female mold and the singlebladed master impeller. The members 22 as they are made are removed from [the mold. If it were desired to cast three such impellers, :18 interblade mold members 22 would be prepared preliminary to initiating casting procedures. To cast a six-bladed impeller, six members 22 and the mold box 12 with its mold cavity 16 are required. These six cores are then arranged in the female mold cavity 16 as indicated in FIG. 7 at 22, 22a, 22b, 22c, 22d and 22a. It will be noted that in each case the pressure surface impression B of the plaster core is located 60 counterclockwise from the surface impression B of the previous plaster core. This leaves a space 24 between each pair of adjacent plaster cores which has the exact dimensions of a blade of the impeller. The plaster cores may be secured in this spaced relation in the cavity 16 by means of pins (not shown) in .a well-known manner.

In summary, then, to make the six-bladed impeller illustrated in FIG. 8, the mold box 12 with its female mold cavity 16 is utilized with the master impeller hub and single master blade to form six inter-blade mold members 22. Each of these members 22 is made separately, as illustrated in FIGS. 3-6, and when finished is removed from the mold cavity. When six of these members 22 have been made, they are then assembled in the mold cavity, without the master hub and blade, as shown in FIG. 7, and the mold is ready to pour.

When the mold, thus prepared, is poured, and the interblade cores 22-22e have been removed, a six-bladed impeller results, as is shown in FIG. 8. In the case of an impeller having a high angle of wraparound of its blades, the interblade core members will of necessity be destroyed in removing them, but this is of small concern since it is relatively easy matter to make a new set from the master impeller for each impeller cast, using the method abovedescribed.

It the impeller is to be used at high temperatures, as for example in a pump for pumping liquid metal, the material 14 used in making the female mold should be made of, or coated with, some heat-resisting material such as one of the ceramics above-referred-to, as the impeller hub and blades will be poured with some such high fusing metal as stainless steel which can withstand these high temperatures.

Instead of pouring the stainless steel directly into the mold as shown in section in FIG. 7, it is possible to pour this mold with wax in molten form. After the wax has hardened and members 22 through 22a have been carefully removed, a male wax pattern results. This is then metal spray-coated, or dipped in a ceramic slurry, to strengthen its surfaces and is used in a female refractory mold similar to that shown in FIG. 2. After the molding material has been packed around the male mold, the wax is removed either by melting or vaporizing. The mold is then ready to be poured with the stainless steel. The particular manner of pouring the mold is not my invention.

As above-described, the impeller has been made without its hub tip 29, which is made separately. One of these tips is shown in FIG. 8, which may be cast or turned, and it will be noted that a threaded shank 28 is provided for attaching the tip 29 to the impeller, the impeller hub 8 being axially bored and tapped to receive the threaded shank 28.

Due to the fact that the transverse shrinkage of the blades cannot be determined as acurately as required for the outside dimensions of the impeller, the master impeller is made with a slight surplus of material on the blade edges which is readily machined off the cast impeller in a simple lathe operation.

It will be evident from the above description that a method has been provided by this invention for making impellers of such complex blade design that it would be very difiicult or even impossible to produce them by prior methods.

It will also be evident that the multibladed impellers, for which this method is particularly advantageous, can be produced as a result of this invention very quickly and very cheaply. The method is particularly advantageous for experimental work when it is desired to run tests on a large number of variations in blade configuration.

Also, it will be clear that by my concept of making all of the interblade cores from a master impeller consisting of a hub and a single blade, I have materially advanced the art of making cast impellers.

Further, it will be evident that as a result of this invention each blade of the impeller, since its critical suction and pressure surfaces were made from a common master blade, is an exact duplicate of each of the other blades of the impeller.

It will also be clear that casting impellers with a large angle of blade wraparound no longer presents insurmountable difficulty since the single blade on the master impeller is readily accessible during shaping of its surfaces.

While for the purposes of illustration 9. six-bladed impeller has been shown, it will be understood that impellers of any desired number of blades may be produced by this method and that the shape and arrangement of the impeller blades may be widely varied without departing from the scope of the invention as defined by the appended claims.

I claim:

1. The steps in making a multiblade cast impeller which consist in generating a master hub having the desired axial curvature and forming one master blade thereon having pressure and suction surfaces of the exact shapes desired, taking a molded impression of the pressure surface of the master blade, indexing the impression about the axis of the hub to the next blade position on the suction side of the master blade so that the pressure surface of the impression occupies the position of the pressure surface of the next blade, making an interblade space core by filling the space between the impression surface and the suction side of the master blade with moldable material, repeating the steps of making an interblade space core until a core has been provided for each interblade space of the impeller, arranging said interblade cores in spaced relation in a female mold shaped to form the outer periphery of the impeller with the surfaces defining the spaces between cores forming the pressure and suction blade surfaces of the mold, and pouring said mold.

2. The steps in making a multiblade cast impeller which consist in making a master consisting of a hub and one blade, using said master to form a female mold cavity commensurate with the outer peripheries of the impeller blades by rotating the master about its axis of rotation in a body of moldable material, using the master to form an interblade core by forming an impression of one surface of the master blade and the adjacent surface of the hub, indexing the impression on the hub to the corresponding position of the next blade on the opposite side of the master blade from that on which the impression was taken, and filling the space between the master blade and the impression with moldable material, repeating the steps of making an interblade core until as many interblade cores have been produced as there are blades in the impeller being cast, arranging said interblade cores in equally spaced relation in said female mold, pouring said mold, removing excess material from the blade edges by turning the casting in a lathe to the exact curvature desired, and securing a hub tip to the casting to complete the impeller.

3. The method of making a multiblade cast impeller which consists in generating a master hub having the desired axial curvature and forming one master blade thereon, taking an impression of one side of the master blade, indexing the impression about the axis of the hub to the next corresponding blade position on the other side of the blade from which the impression was taken, filling the space between the impression and said other side of said blade to form a core of the space between two adjacent blades, repeating the steps of making an interblade core until a core has been provided for each inter-blade space of the impeller, and using said cores in a female mold cavity to cast the impeller.

4. The steps in making a multiblade cast impeller which consist in making a master consisting of a hub and one blade, said hub being formed to the required axial curvature from one end of the blade to the other and said blade having its suction and pressure surfaces made to the exact surfaces desired, using said hub and blade for producing as exact duplicates all the blades of the finished impeller by first making a female mold by rotating said master about its axis of rotation in a body of moldable material to form a basic female mold cavity, using said master to form the required number of interblade cores for the impeller to be cast, securing the interblade cores in equally spaced relation about the axis of said female mold, the spaces between cores representing the volume of the blades between their suction and pressure surfaces, and pouring said mold.

5. The steps in making a multiblade cast impeller which consists in making a master of an easily workable material consisting of a hub and a single blade, said hub being formed to the desired axial curvature and said blade having its pressure and suction surfaces shaped to the desired curvature, rotating said master about its axis of revolution in a body of moldable material to form a female mold, the side wall of which conforms to the tip configuration swept by the blades, taking an impression of one surface of the master blade and the adjacent hub surface while the master is in said female mold, removing the impression and indexing it on the master into the next blade position on the opposite side of the master blade from which the impression was taken, while the master is in said female mold filling the space between said impression and the other side of the blade to form an interblade core, making interblade cores in this fashion until as many cores have been made as there are blades in the impeller being cast, and securing said interblade cores in equally spaced relation in said female mold ready to form said impeller.

References Cited in the file of this patent UNITED STATES PATENTS 

3. THE METHOD OF MAKING A MULTIBLADE CAST IMPELLER WHICH CONSISTS IN GENERATING A MASTER HUB HAVING THE DESIRED AXIAL CURVATURE AND FORMING ONE MASTER BLADE THEREON TAKING AN IMPRESSION OF ONE SIDE OF THE MASTER BLADE, INDEXING THE IMPRESSION ABOUT THE AXIS OF THE HUB TO THE NEXT CORRESPONDING BLADE POSITION ON THE OTHER SIDE OF THE BLADE FROM WHICH THE IMPRESSION WAS TAKEN, FILLING THE 